Diamond Mines of the World: Brazil

History of Brazilian Diamond Mining

After a two thousand year run, India's Golconda diamond mines were nearly depleted by the early 1700s. Fortunately, a new find in the Portuguese colony of Brazil in 1725, helped to re-invigorate the European diamond trade. During Brazil's "diamond rush" years (1725-1860), the Portuguese crown declared a "royal monopoly" on all diamond mining in Brazil, placing the industry under state-regulated control.

To obtain a mining concession from the Portuguese government, a gold deposit was required to cover any future taxes that would be levied on production. The tax, known as the "Royal Fifth," was a hefty 20 percent, based on the value of expected proceeds from the mine. During this period, Brazil was able to produced somewhere between 50,000 and 250,000 carats of rough diamonds per year.

Mining and the Slave Trade

Alluvial mining in Brazil was a labor-intensive vocation, and as such, slaves imported from Africa were used extensively in mining operations. The capital city of Salvador De Bahia (est. 1549), on the Bahia de Todos os Santos ("All Saints Bay") in Bahia, was a global hub for the Portuguese slave trade, and to this day, the state of Bahia has the highest concentration of blacks in Brazil.

Brazilinan cascalhão mining (c. mid-1700s)

Diamantiferous sands and gravel called cascalho, or cascalhão were hand-dug from river ledges and beds, scooped out of the river bottom by divers (escafandro), or dug from hillsides (engrunada or gruta). Then the diamond-bearing alluvium was washed in sluices of running water, washed again in wooden basins called faísca or lavagem, and finally picked through by hand [3]. The cascalhão occurs in high river-bank ledges, as a combination of gravel and sand, but river-bottom gravel deposits typically lay beneath a bed of clay and silt.

At first, Brazilian diamonds were not as desirable as their Indian counterparts [4], and the fist few years of mining yielded smaller-sized stones. As the supply of Indian diamonds dried up however, Brazilian stones gained in popularity. By the mid 1700s, Brazilian diamonds were flooding the European market, and prices fell precipitously, but this was reversed as Brazilian supplies began to dry up in the early 1800s. Brazil's largest rough diamond to date is the "Star of the South," a 254 carat stone found in 1854.

Alluvial deposits in Brazil were created by diamantiferous material being transported from its primary source, within kimberlite intrusions along the Amazonian Cráton to the north, and the San Francisco Cráton in Minas Gerais [14]. There are also diamond-bearing kimberlite bodies in the regions of Mato Grosso and Rondônia.

Diamantina in Minas Gerais

Miners prospecting for gold along the Rio Jequitinhonha river, near the town of Tejuco (now Diamantina) in the Minas Gerais region, made Brazil's first diamond discovery in 1725. By 1740, there was a major diamond rush to Minas Gerais' Rio Abaete and Rio Jequitinhonha alluvial deposits, and mining in the region reached its peek between 1785 and 1807.

Mato Grosso's Alluvial Diamond Fields

The Portuguese government took possession of the Mato Grosso territory in 1748, creating a Colonial Captaincy so as to fully exploit the mineral wealth of the region. Mining exploration was heavily regulated by the Portuguese Crown during the 1700s, and all extracted minerals were subject to high taxation.

Mato Grosso's alluvial diamonds were first discovered in the Morro Vermelho formation, near the mining town of Diamantino. By 1847, both diamonds and gold were mined-out in the area, and by 1852, the Diamantino prospect was abandoned, bankrupting the Mato Grosso Mining Society.

Chapada Diamantina in Bahia

In 1842, large diamond deposits were discovered along the banks of the rio Mucugê in the mountainous region of Chapada Diamantina ("Diamond Highlands"), in the Brazilian state of Bahia. This created a diamond-rush to the region, causing a new glut in the European market.

Diamonds in Chapada Diamantina's Serra da Sincorá (Cincora) region (aka Lavras Diamantinas) occur in river gravels and sands (cascalhão) along the banks of the rio Mucugê, which is a tributary of the rio Paraguaçu (Paraguassu river). Within the Chapada Diamantina sits the Circuito do Diamante ("Circuit of the Diamonds"), surrounded by the towns of Andaraí, Mucugê, Palmeiras, and Lençóis.

By 1901, around 5,000 African slaves worked in the Bahia mines at Serra da Sincorá. The Sincorá region is one of the few locations on earth that carbonado is found. Carbonado (aka "carbon diamond" or "black diamond") is a rare, semi-porous, black polycrystalline variety of diamond.

The Chapada Diamantina has a dramatic landscape with high plains, table-top mesas, and steep cliffs or towers known as tepuy. Before the arrival of the Portuguese in the 1800s, the only local inhabitants of the region were indigenous Indians from the Maracas and Cariris tribes. In 1985, the Chapada Diamantina region was made into a National Park, with its headquatrers in Palmeiras.

Brazil's Recent Diamond History

In the 1960's, near Mato Grosso's capital of Diamantino, the "Mato Grosso Diamond Project" (a 63,000-hectare claim block) created a diamond-rush to the area. To date, more than 50 kimberlite pipes have been located, many of which are the most likely source for the region's historic alluvial deposits [5].

In 1999, nearly 3,000 itinerant miners (diamond diggers, or garimpeiros) illegally entered the protected Cinta Larga ("broad belt") Indian reservation to mine for diamonds. The Cinta Larga reservation lies between the states of Rondônia and Mato Grosso, along the Bolivian boarder. Mining was forbidden within the 'Roosevelt Reservation' in order to preserve the indigenous Cinta Larga people's homeland, but the Cinta Larga are allowed to engage in small-scale prospecting called garimpagem, if the labor is done exclusively by indigenous Indians. Federal Police evicted the garimpeiros, but the government estimates that as much as $50 million worth of illegally mined diamonds were smuggled to Belgium.

The Cinta Larga attacked a group of illegal prospectors in April of 2004, killing 41 of them [7]. Since the incident, tensions in the region have eased, and in October 2004, Brazil received accreditation to obtain a Certificate of the Kimberley Process. Diamond mining within the Roosevelt Reservation could be worth an estimated $3.5 billion annually.

Future Diamond Mining in Brazil

The most promising locations for any future Brazilian diamond mining activity are in the states of Matto Grosso and Bahia, and in recent years diamond mining activity has picked up within these regions. Diagem Inc. in cooperation with Rio Tinto (Rio Tinto Desenvolvimentos Minerais Ltda) is still surveying for new diamond finds in Brazil [9]. There have been several promising finds at its 'Collier-04' kimberlite pipe, located in the Juina diamond district of Mato Grosso.

Exploration in the Diamantina, Regis, Santo Antonio, and Serra da Canastra regions of Minas Gerais is currently being conducted by Brazilian Diamonds Limited, CODEMIG, and Mineração Rio Novo Ltda.